Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G11/00—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G1/00—Production of liquid hydrocarbon mixtures from oil-shale, oil-sand, or non-melting solid carbonaceous or similar materials, e.g. wood, coal
  • C10G1/10—Production of liquid hydrocarbon mixtures from oil-shale, oil-sand, or non-melting solid carbonaceous or similar materials, e.g. wood, coal from rubber or rubber waste

Definitions

• the present invention relates to a process for cracking polymers, especially olefin polymers, whether virgin or waste, in order to produce lower hydrocarbons so as to conserve valuable resources.
• the present invention is a process for cracking a polymer in a fluidised bed reactor into vaporous products comprising primary products capable of being further processed characterized in that the vaporous products are treated to generate a primary product substantially free of a high molecular weight tail (hereinafter HMWT) comprising hydrocarbons having a molecular weight of at least 700 as measured by gel permeation chromatography.
• HMWT high molecular weight tail
• polymer By the expression “polymer” is meant here and throughout the specification virgin (scrap generated during processing of the plastics into the desired article) or waste after the plastics has performed its desired function.
• the term “polymer” therefore includes polyolefins such as polyethylene, polypropylene and EPDM with or without one or more of other plastics eg polystyrene, polyvinyl halides such as PVC, polyvinylidene halides, polyethers, polyesters and scrap rubber.
• the polymer stream may contain small amounts of labelling, closure systems and residual contents.
• the fluidised bed used is suitably comprised of solid particulate fluidisable material which is suitably one or more of quartz sand, silica, ceramics, carbon black, refractory oxides such as eg zirconia and calcium oxide.
• the fluidising gas is suitably chosen so that it does not oxidise the hydrocarbons produced. Examples of such a gas are nitrogen, the recycled gaseous products of the reaction or refinery fuel gas.
• the recycled gaseous products used are suitably components of the vaporous products emerging from the fluidised bed which are separated using a flash or other suitable liquid-gas separation unit at a set temperature -50° to 100° C.
• Refinery fuel gas referred to above is a mixture comprising hydrogen and aliphatic hydrocarbons, principally C 1 to C 6 hydrocarbons.
• the fluidising gas may contain carbon dioxide over a wide range of concentrations.
• the fluidisable material suitably comprises particles of a size capable of being fluidised, for example 100 to 2000 ⁇ m.
• the heat for the reaction is suitably brought in by the fluidising gas.
• the polymer to fluidising gas weight ratio is suitably in the range from 1:1 to 1:20, preferably 1:3 to 1:10.
• the polymer can be added to the fluidised bed either as a solid or in the form of a melt but is preferably added in the solid form.
• the fluidised bed may contain materials to absorb acidic gases or other contaminants in the polymer feed.
• vaporous products comprising saturated and unsaturated aliphatic and aromatic hydrocarbons, and containing less than 25% w/w, preferably less than 20% w/w of gases comprising C 1 -C 4 hydrocarbons, hydrogen and other carbonaceous gases; and containing no more than 10% w/w of aromatic hydrocarbons associated with the weight of polyolefin polymers in the feed.
• the vaporous products include the "primary products” which are the products which separate as solids and/or liquids from the vaporous products emerging from the fluidised bed polymer cracking reactor when that reactor is cooled to temperatures around ambient (eg -5° to +50° C.) ⁇
• a high molecular weight tail (hereafter “HMWT)" is meant here and throughout the specification a product which comprises hydrocarbons having a molecular weight (Mw) of at least 700 as measured by gel peremeation chromatography (GPC).
• a feature of the present invention is that the proportion of the polymer which is low conversion of the polymer into vaporous products having less than 4 carbon atoms and the substantial absence of aromatic hydrocarbons.
• a smear of a sample was made up in a 4 ml vial with trichlorobenzene at about 0.01% w/w concentration. This was then held in an oven at 140° C. for 1 hr. This sample was then run on GPC. The trichlorobenzene was used as the solvent to carry the sample through the columns of the GPC for analysis using the following apparatus:
• Mi average molecular weight in increment i
• N T number of molecules in total sample
• N i number of molecules in increment.
• steam cracker is meant here and throughout the specification conventional steam crackers used for cracking hydrocarbons, waxes and gas oils for producing olefins and comprising a preliminary convective section and a subsequent radiant section, the cracking primarily occurring in the radiant section and the cross-over temperature between the convective section and the radiant section of the cracker suitably being in the range from 400°-750° C., preferably from 450 °-600° C.
• the primary products fed eg to the convection section of a steam cracker ⁇ contain no more than 15% w/w of the HMWT, suitably less than 10% w/w, preferably less than 5% w/w of HMWT in the total primary products fed.
• the amount of HMWT in the primary products from the fluidised bed polymer cracking step can be minimised in various ways. For instance, one or more of the following methods can be used:
• the vaporous products leaving the fluidised bed may be fractionated either in situ or externally to separate the HMWT content thereof and the treated HMWT fraction can be returned to the fluidised bed for further cracking.
• the fluidised bed reactor can be operated under pressure in order to maximise the residence time of any large molecules eg HMWT in the reactor thereby enabling these larger molecules to be cracked to smaller molecules.
• the pressure used is suitably in the range from 0.1-20 bar gauge, preferably from 2-10 bar gauge.
• the use of pressure in the fluidised bed can also enable control of volume flow through the reactor thereby allowing enhanced residence time for the polymer and the cracked products in the fluidised bed thereby reducing the HMWT in situ.
• a catalytic fluidised bed can be used to reduce HMWT in situ.
• the entire particulate solid used as the fluidised bed may be an acidic catalyst although the acidic catalytic component is suitably less than 40% w/w of the total solids in the fluidised bed, preferably less than 20% w/w, more preferably less than 10% w/w.
• the fluidised bed is suitably operated at a temperature from 300°-600° C. preferably at a temperature from 450°-550° C.
• the primary products free of the HMWT can be further processed to other hydrocarbon streams in units designed to upgrade the value of products derived from crude oil.
• Such units are normally found at an oil refinery and include, in addition to steam crackers, catalytic crackers, vis-breakers, hydro-crackers, cokers, hydro-treaters, catalytic reformers, lubricant base manufacturing units and distillation units.
• a fluidised quartz sand bed reactor fluidised with nitrogen was used to crack polyethylene (HDPE 5502XA ex BP Chemicals Ltd) except in (i) CT 3 where the polymer used was a mixture of 90% HDPE and 10% PVC and (ii) CT 8 where the polymer used was a mixture of 70% HDPE, 15% polystyrene, 10% PVC and 5% polyethylene terephthalate.
• quartz sand (180-250 ⁇ m size) (about 50 ml in the unfluidised state) was fluidised in a 45 mm outside diameter quartz tube fluid bed reactor.
• the reactor was provided with a three zone tubular furnace for heating to the required temperature (400°-600° C.), the first zone being used to pre-heat the fluidising gas.
• Nitrogen was used as the fluidising gas at 1.5 liter/min (measured under laboratory conditions).
• the bed was operated at atmospheric pressure.
• Polymer pellets (size typical of pellets used as feed for plastics processing) were fed into the bed with a screw feed at the approx. rate of 50 g/h.
• Gaseous products first passed down a section kept at 80°-120° where the majority of the product was collected. The gases passed down an air cooled section after which they were sampled. When a full mass balance was required, all the gases were trapped in bags at the end of the apparatus.
• the non-gaseous product from these experiments was a wax which melts at about 80° C.
• a 20% mixture of the 480° C. run (CT 2) is a typical Naphtha (see analysis below) and gives a thick slurry at room temperature that clears at 70° C.
• the wax from CT 6 was melted and fed into the reactor set as for CT 1-8 above.
• CT 1-8 To illustrate the value of catalysts to this process the conditions in CT 1-8 were modified by replacing 8 g of the sand with 8 g catalyst sieved to a suitable size to be compatible with the fluidisation in the bed. This gave a 10% by weight mixture of sand and catalyst.
• the collection system was modified with an 50 mm diameter Aldershaw distillation column with 10 trays filled and topped up with water. This replaced the section at 80° to 120° C. and the air condenser.
• the polymer fed to the fluidised bed was polyethylene (grade HDPE 5502XA, ex BP Chemicals Ltd) except in Example 3 which used the same polymer as in CT 3; in Example 4 which used the same polymer as in CT 8; and Example 6 in which a mixture by weight of polyethylene (97% grade HDPE 5502XA) and titanium dioxide (3%) was used.
• Example 9 The product from Example 9 was analysed by a slightly different GPC technique.
• Example 2 gave a soft wax which melts at about 70° C.
• a 20% mixture of this in naphtha as above gives a thin cream at room temperature that clears at 60° C.
• Example 9 gave a cloudy liquid at room temperature which settled with time to give a clear top section and some wax present in the lower half.
• a 20% mixture of this in naphtha as above gives a slightly hazy solution at room temperature that clears fully at 50° C.
• Example 10 gave a hazy liquid at room temperature.
• a 20% mixture of this in naphtha as above gives a clear solution at room temperature.
• Example 12 To illustrate the performance in the steam cracking stage of the product produced with a catalyst in the bed, the product of Example 12 was mixed 50/50 with naphtha and passed through a micro-cracker at 800° C. at 20 psig using a feed rate of 2.0 ml/hr and a helium flow rate of 6.0 liters/hr at NTP.
• a fluid bed reactor of 78 mm diameter was charged with Redhill 65 sand (ex Hepworth Minerals and Chemicals Ltd) and fluidised using nitrogen at a flow rate of 15 1/minute (@ NTP) and heated to a temperature of about 530° to 540° C.
• Polyethylene (HDPE 5502XA ex BP Chemicals Ltd) was charged at about 200 g/hour.
• This reactor had much shorter residence time than the reactor described in CT 1 and thus gave higher Molecular weight tail for the same operating conditions of pressure and temperature--Mw for this apparatus at 530° C. and 1 bar gauge is predicted to be 900 (cf CT 6 at 501).
• the heavy molecular weight tail was halved by increasing the pressure from 1 bar gauge to 2 bar gauge (38.3% to 19.1%). These results have been extrapolated using a reliable computer model to a fluid reactor at 550° C. and 3 bar gauge with longer residence time and recycling a portion of the gas from the cracking of the polymer as the fluidising gas to show that no more than 0.04% is HWMT and at 9 bar gauge no more than 0.006% HMWT.
• the data for tail above a molecular weight of 500 are 0.5% and 0.06% respectively.
• the data for tail above a molecular weight of 350 is 7.5% and 1.2% respectively.

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• Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Processing Of Solid Wastes (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
• Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)

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• 1993
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• 1996
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